It's great that you read this book. It's unfortunate that you were expecting them to be monsters. I think the modern take on Nazi Germany as pure evil is the most dangerous one we have. They were no different than anyone else, which is why their tale should be told as a cautionary one.
My favourite books on the same topic are "They Thought They Were Free" and "Ordinary Men".
We all walk the line between moral and monster every day. History wiill one day say of us, "They seemed so ordinary, though we know they were monsters."